For manufacturing a protective insulation film of a flexible printed circuit board, polyimide resin, polyurethane resin, polyamideimide resin or epoxy resin is generally employed. These resins are utilized in the form of a curable resin composition, if necessary, after addition of a curable compound.
The protective insulation film preferably has high flexibility, high bendability and low warping property in addition to high heat resistance, high resistance to chemical materials, and high resistance to solvents.
U.S. Pat. No. 6,335,417 B1 describes a modified polyimide resin which can give an article having high heat resistance, good pliability, and low warping property. The modified polyimide resin comprises recurring units composed of polyimide units containing polybutadiene moiety and units of residue derived from diisocyanate.
JP-A-2-191623 describes a thermosetting resin composition comprising a modified imide oligomer having a hydroxyl group at each terminal and an epoxy group-containing compound. The modified imide oligomer is prepared by reacting a biphenyltetracarboxylic acid compound, an aromatic amine compound, and a monoamine compound having at least one hydroxyl group in a solvent.